1. Field of the Invention
This invention relates to a method of stabilizing the peptide superoxide dismutase with fragments of casein. This invention further relates to pharmaceutical compositions containing the stabilized superoxide dismutase, and a method of scavenging free radicals from a mammalian body by introducing the pharmaceutical composition into the body orally.
2. Discussion of Related Art
The use of peptides in therapeutic applications has been studied in recent years. See, for example, Steinman, "Development of Antigen-specific Therapies for Autoimmune Disease", Mol. Biol. Med., vol. 7, pps. 333-339 (1990), Mohapatra et al. "In Pursuit of the `Holy Grail`: Recombinant Allergens and Peptides as Catalysts for the Allergen-specific Immunotherapy", Allergy, vol. 50 (suppl 25), pps. 37-44 (1995), and Adorini et al., "Approaches Toward Peptide-based Immunotherapy of Autoimmune Diseases", Springer Seminars in Immunopathology, vol. 14, pps. 187-199 (1992).
Superoxide dismutase (SOD) is a peptide known to act as a scavenger of free radicals, in particular the superoxide radical O.sub.2.sup.-, in a mammalian body. See, for example, Burnham, "Polymers for Delivering Peptides and Proteins", Am. J. Hosp. Pharm., vol. 51, pps. 210-218 (1994). As discussed in that article, the level of oxygen free radicals present in a mammalian body increases during times of stress on the body, for example as a result of lung diseases, thermal injury, ischemia and repurfusion, inflammation and organ transplantation, likely as a result of the body not being able to produce sufficient levels of SOD. The level of oxygen free radicals present in the body also increases gradually as the body ages, again likely due to the gradual decrease in SOD production with aging. Increased levels of oxygen free radicals within a mammalian system is dangerous in that these radicals are known to damage a variety of body tissues, for example by attacking and bursting healthy cells.
To combat increased levels of oxygen free radicals in the mammalian system, treatments with SOD are known. See, for example, Burnham, supra at p. 215. Such methods introduce the SOD into the body via injection, that is, directly into the veins or muscles of the body. This is because SOD is very susceptible to attack and breakdown by proteases present in the digestive tract and in the circulatory system of mammalian bodies, thereby greatly reducing the effectiveness of oral administrations of SOD. Native SOD has a half-life on the order of only 10-40 minutes, and thus is typically injected into a mammal in an effort to maximize the scavenging efficiency of SOD prior to breakdown.
Burnham, supra, proposes a method of increasing the half-life of various proteins and peptides, including SOD, by binding a polymer, in particular polyethylene glycol, to the sites of the molecule that cause the body to recognize the molecule as foreign and thus break it down. Burnham acknowledges that the polymers decrease the biological activity of the protein or peptide, but at the same time greatly increase the half-life of the molecule. Burnham does not disclose oral ingestion of SOD compositions.
Xian et al. "Degradation of IGF-I in the Adult Rat Gastrointestinal Tract is Limited by a Specific Antiserum or the Dietary Protein Casein", Journal of Endocrinology, vol. 146, pps. 215-225 (1995), proposes a method of protecting orally ingested IGF-I against proteolytic degradation prior to the peptide being taken up and acting to stimulate gut growth and repair. The peptide was protected effectively in the stomach and colon of rats prior to take up in the intestines by either complexing the peptide with an IGF-I antiserum, or by complexing the peptide with very high concentrations of the whole proteins casein, BSA or lactoferrin.